Polycyclic aromatic hydrocarbons (PAHs) are a main component of petroleum that includes some of the most toxic, carcinogenic, genotoxic, and mutagenic hydrocarbons. Their molecular structures vary as combinations of multiple fused benzene rings that become more complex with size and aromaticity. As the molecular weight (MW) of PAHs increases, so does their potency with dibenzo[a,l]pyrene, a six-ring PAH with MW of 302 g mol-1, considered to be the most potent carcinogen of all PAHs. To date there is a critical gap in the research regarding the environmental occurrence and distribution of these high molecular weights (HMW) PAHs due to difficulties in analytical separation and detection. As a result, the behavior of these "hidden" organic compounds in a natural ecosystem and the microbial metabolic activities that may degrade them are as yet unknown. Recent advances, however, in state-of-the-art detection and quantification of HMW-PAHs using high-resolution vibrational spectroscopy by Co-PI Campiglia open new and exciting avenues of study for these "hidden" PAHs. As microorganisms are the primary drivers of petroleum degradation in the environment, microbial biodegradation studies of HMW-PAHs MW ≥ 302 will be conducted in conjunction with analytical identification and quantification of these PAHs and their metabolites. This project will address research Theme Two with the goal to examine the biodegradation of "hidden" HMW-PAHs MW ≥ 302 by (1) individual microbial isolates and (2) sediment microbial communities to determine biological degradation pathways and identify metabolic intermediates using both culture-dependent and culture-independent (i.e., metagenomics) methods.
Research Objectives and Goals: The objectives of the proposed study are to (1) determine the ability of known PAH-degrading bacterial species to degrade HMW-PAH MW ≥ 302 compounds in pure cultures and identify the metabolic degradation products using fluorescence spectroscopy with emphasis on PAH-metabolites that are known to be carcinogenic; and (2) identify new, environmentally relevant bacteria capable of degrading HMW-PAH MW ≥ 302 compounds through sediment enrichment incubations using both culture-dependent isolation techniques and culture-independent techniques (i.e., metagenomics). These objectives will be achieved through an integrated research program coupling microbiological and state-of-the-art analytical techniques in order to investigate the microbial degradation of recalcitrant HMW-PAH organic compounds with a goal to better understand the microbial response to oil spills.
Potential Scientific and Societal Impact: The extent to which human activities are influencing coastal ecosystems is an issue of regional and national importance. Oil spills cause considerable alteration to the functioning of these systems and improving our understanding of how recalcitrant, highly toxic hydrocarbons, which may build up in sediments over long periods of time, are naturally degraded will add to our overall knowledge of their fate in natural systems. This project will build on and leverage contributions of our prior research activities directed at understanding microbial responses to oil in the Gulf of Mexico as well as developing state-of-the-art analytical techniques to measure these "hidden" PAHs and their metabolites. The project will provide training opportunities for two Ph.D. graduate students and 4-6 undergraduate students. This proposed research study will contribute directly to the ultimate goal of the Gulf of Mexico Research Initiative, which is "to improve society's ability to understand and respond to the impacts of petroleum pollution and related stressors of the marine and coastal ecosystems, with an emphasis on conditions in the Gulf of Mexico."